The present invention relates to data processing systems and more particularly to systems which include a type of prefetch capability.
In large scale and multiprocessor systems, processor performance has been improved by providing a cache store or high-speed buffer storage unit between the system's large main storage unit or backing store and the central processing unit. To further increase the system performance, prior art data processing systems have also included a prefetched capability in which a next sequential line of data is fetched by the cache store automatically after supplying the line of data requested by the central processing unit.
A disadvantage of the above systems was that such systems did not take into account conditions which alter the basic philosophy that the next sequential line should be prefetched immediately from main store. To overcome the disadvantage mentioned, one system has included algorithms for prefetching a next sequential line from main storage to the high-speed buffer and algorithms for replacement of existing lines in the high-speed buffer which may be dynamically modified relative to the type of program being executed by the use of a system console unit. More particularly, the system includes an operating state register which corresponds to the variables of the prefetch control algorithm. Such variables are based upon references to preceding lines being requested.
While the above arrangement provides for variation as to accessing a next sequential line of data before a request is made, it has the disadvantages of basing the prefetch request upon an arbitrary circumstance relating to the particular byte or portion of a line being referenced by a previous request. While this is advantageous in certain types of operations, it could result in decreased performance in other cases. More specifically, automatic accesses can increase memory congestion.
Accordingly, it is a primary object of the present invention to provide an improved data processing system with a type of prefetch capability.
It is another object of the present invention to provide an improved data processing system with a prefetch capability suitable for use in either a high speed processing system or a multiprocessing environment.